Spiders can perceive sound, but their detection method differs vastly from the auditory systems of mammals. Lacking eardrums, spiders rely on an incredibly sensitive system that detects the physical movement of air particles—a fundamental component of sound. This function is a highly specialized form of mechanoreception, allowing them to sense minute airborne vibrations and perceive their acoustic environment, often from significant distances.
Detecting Airborne Sound
Spiders sense sound based on particle velocity—the actual displacement of air molecules caused by a sound wave—rather than the pressure changes registered by human ears. This allows the spider to use its entire body, especially its eight legs, as an array of sophisticated vibration detectors. Some species can detect these airborne cues from several meters away.
This sensory ability covers a wide spectrum of frequencies, up to 10 kilohertz (kHz). Low-frequency sounds (80 to 130 Hz) are particularly important, as they characterize the wingbeats of flying insects or nearby predators. Since low-frequency acoustic signals travel farther and lose less energy, this broad detection range provides spiders with an early warning system.
The Role of Specialized Leg Hairs
This detection is centered on two specialized sensory organs located primarily on the spider’s legs: trichobothria and slit sensilla.
Trichobothria
Trichobothria are extremely fine, non-tapered hairs that emerge from the exoskeleton, acting as microscopic antennae for air movement. Each hair is set within a flexible, cup-shaped socket, allowing it to pivot freely with the slightest current or vibration. This mechanism makes them so delicate that they can be excited by air movement as slow as one millimeter per second.
They are capable of detecting physical displacements of air particles smaller than a single nanometer. The socket arrangement provides directional information, allowing the spider to pinpoint the source of the sound.
Slit Sensilla
The slit sensilla consists of minute, crack-shaped slits in the cuticle that measure the strain on the exoskeleton. Often found near joints, this mechanoreceptor complements the trichobothria’s detection of air displacement.
How Spiders Use Sound Detection
Spiders use this auditory ability for both hunting and defense.
Hunting and Foraging
Net-casting species, such as the ogre-faced spider, use sound to precisely locate airborne prey. The detection of specific low frequencies, like those made by insect wings, triggers a rapid, backward strike to ensnare the flying insects.
Defense and Warning
Sound detection enables the spider to detect the approach of larger animals or predators like parasitic wasps. Upon sensing a threatening stimulus, many spiders exhibit an acoustic startle response, instantly freezing as an anti-predatory camouflage behavior.
Web Amplification
In web-building species, the silk web functions as a massive external acoustic antenna, sometimes 10,000 times larger than the spider’s body. Orb-weavers can actively tune the tension of the silk strands by adjusting their posture, filtering for specific sound frequencies and customizing their sensory reception.